LightZone is similar to Darktable, Rawtherapee, Photivo etc. If your shooting RAW photos they are worth a look for processing between camera and Gimp. To take full advantage the learning curve is high for these programs. LightZone seems to have an interesting 'Zone' method. Here is another review of
LightZone.
UFRaw is a fairly decent easy to use, although not as full featured, alternative for Gimp. UFRaw works quite well for my basic needs or else I use RawTherapee but I might give LightZone 4 a go.
A Review of FLOSS Raw Processors, Part 1This article is a very in depth look at raw processors, it doesn't cover LightZone but it's definitely worth a read if you interesting in learning more about raw processors features and how they work. It compares: dcraw, Darktable, the digiKam raw processor, Photivo, Rawstudio, RawTherapee, and UFRaw.